In powertrain systems for motor vehicles, torque-transmitting mechanisms such as clutches are used to selectively engage gear sets for the transmittal of torque from the motor through the transmission to the drive shafts to propel the vehicle. Hydraulically operated pistons are used to actuate the engagement or disengagement of the clutches.
Hydraulic pressure may be supplied to a hydraulic piston by a hydraulic fluid pump drawing hydraulic fluid from a hydraulic fluid reservoir. Upon the loss of hydraulic pressure, due to power or pump failure, the hydraulically operated piston may return to its default position resulting in the unintentional engagement or disengagement of the clutch, resulting in potential damage to the powertrain system.
Thus, there is a need for a mechanism to retain the hydraulic piston of a clutch in a predetermined position in the event of a failure of equipment or hydraulic system to prevent damage to the powertrain.